<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .item-container{
            display: flex;
            justify-content: center;
            width: 600px;
            height: 600px;
            background-color: palevioletred;
        }

        .item{
            /*width: 200px;*/
            height: 200px;
            background-color: palegreen;
        }
    </style>
</head>
<body>
<div class="item-container">
    <div class="item">hello world</div>
</div>
</body>
</html>
